FIG. 1 shows a perspective view of a prior art rotational positioning system 10. As shown, system 10 includes a positioning component 20. As will be discussed in greater detail below, in operation positioning component 20 is used to control the position of a positioned component 30. Rotational positioning systems such as system 10 illustrated in FIG. 1 are well known in the art and may be used, for example, to control the location of read/write heads of hard disk data storage systems during servo track writing.
In system 10, positioning component 20 includes a rotationally mounted arm 21, an actuator 23, and a position sensor 25. Arm 21 is rotationally mounted so that it may rotate in the directions indicated by arrow A—A in FIG. 1. Actuator 23, which may be implemented, for example, using a voice coil motor, is coupled to arm 21 so as to control the rotational orientation of arm 21. Sensor 25, which may be implemented, for example, using an optical sensor, senses the rotational orientation of arm 21. Interface component 50 is disposed at one end of arm 21 and is designed to contact positioned component 30. Interface component 50 is generally implemented as a relatively rigid rod or pin.
In operation, system 10 controls the position of positioned component 30 by using interface component 50 to push or follow positioned component 30 to desired locations. System 10 uses sensor 25 to sense the position of interface component 50 (i.e., by sensing the position of arm 21 to which component 50 is attached) and uses actuator 23 to move interface component 50 to desired locations.
In FIG. 1, the positioned component 30 is shown as including an arm 33, a bearing structure 35, a biasing element 37, and a target feature 31. Arm 33 is rotationally mounted so that it may pivot about a point defined by bearing structure 35 in the directions illustrated by arrow A—A. Target feature 31 is disposed at one end of arm 33. In FIG. 1, target feature 31 represents the read/write heads of a hard disk data storage system. Biasing element 37 operates to bias arm 33 so that arm 33 is biased in the direction of the interface component 50.
In operation, system 10 controls the location of target feature 31 by using interface component 50 to push arm 33 to desired locations. Biasing element 37 insures that arm 33 remains in intimate contact with interface component 50.
Ideally, the positioned component 30 always remains in contact with the positioning component 20 so that the location of the target feature 31 may always be controlled by controlling the location of interface component 50. However, one problem associated with prior art positioning systems such as system 10 is that, at high operating frequencies, including those above a resonant frequency, the response of the positioned component may become decoupled from the input of the positioning component. In the case of system 10 shown in FIG. 1, rapid movements of positioned component 20 may cause arm 33 to become decoupled above the natural frequency of the system from interface component 50. In addition, the positioned component 30 may not settle acceptably after movement of positioning component 20, but may instead oscillate about a desired position for an undesirable period of time. Also, in high frequency systems in which the desired level of control is measured in small units, such as nanometers, the inertial and spring like qualities of components of the positioning system may adversely affect system performance. These qualities of the system may exacerbate (1) the decoupling of the positioned component from the positioning component when the system is operating at high frequencies and (2) the oscillation of the positioned component about a desired position.
FIG. 2 illustrates a prior art approach for suppressing oscillation (or ringing) of the target feature in rotational positioning systems. More specifically, FIG. 2 shows a prior art rotational system 10′, which is substantially identical to system 10 (shown in FIG. 1), except that the interface component 50 of system 10′ additionally includes a pad 55. Pad 55 is fabricated from a dampening material and is attached to the end of interface component 50. Pad 55 is disposed in the system 10′ so that it, rather than interface component 50, makes contact with positioned component 30. The pad 55, therefore, is connected in “series” between the interface component 50 and the positioned component 30 so that the pad 55 itself contacts the positioned component 30. To review, in system 10 (FIG. 1), the relatively rigid interface component 10 directly contacts positioned component 30, and this contact causes positioned component 30 to move in response to any movement of interface component 50. In contrast to system 10, in system 10′, the pad 55 rather than the interface component 50 contacts the positioned component 30. Although motion of interface component 50 in system 10′ still causes movement of positioned component 30, the contact between components 50 and 30 is buffered through pad 55.
Use of pad 55 in system 10′ advantageously reduces oscillation of the target feature 31. However, use of pad 55 in system 10′ also disadvantageously reduces the effective interconnecting spring stiffness between the positioning component 20 and the positioned component 30. This reduction in the effective interconnecting spring stiffness decreases the frequency at which the location of the positioned component 30 will decouple from the location of the positioning component 20. In addition, the properties of the pad 55 may change over time or operational conditions, e.g., with temperature changes, or with stroke range. As a result, the position of the target feature 31 may become indeterminate as the properties of the pad 55 change.
FIG. 3 illustrates a prior art linear positioning system 10a in which a relatively rigid interface component 50a of the positioned component 20a directly contacts the positioned component 30a. FIG. 4 illustrates a prior art linear positioning system 10a′ in which a dampening pad 55a′ is disposed between interface component 50 and the positioned component 30. It will be appreciated that systems 10a (FIG. 3) and 10a′ (FIG. 4) suffer from the same deficiencies discussed above in connection with systems 10 (FIG. 1) and 10′ (FIG. 2), respectively. For completeness, a brief description of system 10a is provided below.
In system 10a, the positioned component 20a includes a translational arm 21a, an actuator 23a, and a position sensor 25a. Arm 21a is translationally disposed so that it may translate in the directions indicated by arrow B—B in FIG. 3. Actuator 23a is coupled to arm 21a so as to control the translation of arm 21a. Sensor 25a senses the translational movement of arm 21a. Interface component 50a, which may be implemented as a relatively rigid rod or pin, is disposed at one end of arm 21a and is designed to contact, or attach to, positioned component 30a. 
In operation, the system 10a of FIG. 3 controls the position of positioned component 30a by using interface component 50a to push or follow positioned component 30a to desired locations. System 10a uses sensor 25a to sense the position of interface component 50a and uses actuator 23a to move interface component 50a to desired locations.
In FIG. 3, the positioned component 30a is shown as including an arm 33a, a bearing structure 35a, a biasing element 37a, and a target feature 31a. Arm 33a is translationally attached so that it may slide along bearing structure 35a in the directions illustrated by arrow B—B. Target feature 31a is disposed at one end of arm 33a. Biasing element 37a operates to bias arm 33a so that target feature 31a is biased towards a home position.
FIG. 4 shows a prior art approach of suppressing oscillation (or ringing) of the target feature in a translational positioning system. More specifically, FIG. 4 shows a prior art translational system 10a′, which is substantially identical to system 10a (shown in FIG. 3), except that the interface component 50a of system 10a′ additionally includes a pad 55a′. The pad 55a′ is similar to the pad 55 of FIG. 2, and is disposed in the system 10a′ so that it, rather than interface component 50a, makes contact with positioned component 30. Much like the use of pad 55 in rotational positioning system 10′ of FIG. 2, use of the pad 55a′ in the translational positioning system 10a′ of FIG. 4 reduces oscillation of the target feature 31a. However, use of pad 55a′ in system 10a′ also disadvantageously reduces the effective interconnecting spring stiffness between the positioning component 20a and the positioned component 30a. Thus, the system 10a′ is subject to the same problems associated with the system 10′ of FIG. 2.
Accordingly, a need exists for a method and system for reducing oscillation of a positioned component in a positioning system while enabling the system to function at sufficiently high frequencies of operation.